Method of producing dimensionally stable polypropylene fibers



1963 M. COMPOSTELLA ETAL 3,106,442

METHOD OF PRODUCING DIMENSIONALLY STABLE POLYPROPYLENE FIBERS Filed July11, 1957 INVENTORS MARIO COMPOSTELLA Fnguco DENT/ a BY ATTORNEY$ UnitedStates Patent This invention relates to textile fibers and moreparticularly to textile fibers of high polymers of propylene composedof, or containing a predominant proportion of, isotactic macromoleculesas defined by Natta et al., and to processes for producing such fibers.

Entirely new polymers of the alpha-olefines CH :CHR

having substantially no branches longer than R have recently beendescribed by G. Natta and his co-workers, and have been defined, by G.Natta in the Journal of Polymer Science, April 1955, vol. XIV, issue No.82, pages 143-154, as linear, head-to-tail polymers composed ofisotactic macromolecules. Isotactic macromolecules as defined by Nattaet al. are macromolecules in which,

at least for long portions of the main chain or for substantially themain chain, the tertiary asymmetric carbon atoms have, on the same chainsection, the same steric configuration, and the main chain of which, iffully extended in a plane, shows all of the R groups bound to thetertiary carbon atoms of the monomeric units making up said chainsection on one side of the plane and all of the H atoms bound to saidtertiary carbon atoms on the opposite side of the plane. The isotacticmacromolecules, which are crystallizable or crystalline, have astereoregular structure of the kind shown in the model below:

(Model of a pontion of the main chain of an isotactic macromolecule ofan alpha-olefin polymer according to Natta et al., arbitrarily fullyextended in a plane, in which the R substituerrts on the tertiary Catoms of adjacent monomeric units are above, and their H atoms arebelow, the plane of the chain.)

ice

paring the elastic properties of nylon yarn with those of a comparableyarn of polypropylene (RF. in the table):

TABLE Elongation 8% 15% Fiber Nylon P.P. Nylon Pl. Instantaneous ElasticRecovery, 100 100 Delayed Elastic Recovery, 98 100 81 95 Theinstantaneous elastic recovery is measured by subjecting the fiber toelongating stress, releasing the stress immediately, and measuring theelastic recovery of the fiber after 60 seconds. measured by subjectingthe fiber to the elongation stress, maintaining the stress for 60seconds, and determining the elastic recovery of the fiber after 60seconds.

The high elastic recovery of our polypropylene fibers is, for manypurposes, a very valuable characteristic. However, it results in certaindifficulties during processing of the fibers and, in addition, the yarntends to shrink strongly when placed in hot water. This tendency toshrink is troublesome during further processing of the yarn and, also,under certain conditions of use of the fibers. Thus, shrinkage of thestretched polypropylene yarns which we produced earlier is eventroublesome in the first winding up. The filament proceeding from thestretching stage, having a high elasticity and being under tension, canbe wound up on a bobbin but shrinks thereon so that the inner windingsare compressed by the outer windings and the filament or yarn is, as aconsequence, differentially strained and has different residualshrinkage capacities along the length thereof which are expended duringfurther processing, e.g., dyeing, and result in uneven effects, such asuneven or non'le-vel dyeing.

The existence of the different strains in the fibers and yarns alsocauses frequent rupture of the yarn when it is unwound from the bobbinunder a constant tension. Moreover, the individual filaments of theyarns are electrized by rubbing and tend to separate from each other, sothat the winding tends to be irregular, increasing the danger of ruptureof the unwinding yarn, as well as of yarn still on the bobbin, duringthe unwinding operation.

An object of this present invention is to provide filaments and yarns ofisotactic polypropylene which are less susceptible to heat-shrinkage(more heat-stable), may have modified elastic characteristics, and whichhave, in general, better mechanical characteristics than is normally thecase.

This and other objects are accomplished by the practice of thisinvention in accordance with which the fibers or yarns are heat-treatedunder special conditions, after stretching thereof, the heat-treatmentbeing performed, at least in part, before the fibers or yarns aretwisted and Wound up. The stretched fibers or yarns are stabilizedagainst excessive shrinkage by heating them at a temperature which maybe somewhat higher than the stretching temperature and while they areheld under a tension The delayed elastic recovery is such that they arenot free to shrink or can shrink to only a controlled extent not greaterthan 15% of the initial length. In order to insure maximum relaxation ofthe strains introduced into the fibers and yarns during the earlierprocessing thereof, the heat-treatment must be carried out at atemperature as close as possible to the first order transitiontemperature for the isotactic polypropylene, which is about 169170 C.

In practice, the stabilization can be carried out continuously. Forexample, the yarn can be stretched at temperatures between 80 C. and 140C. and then held under conditions of non-shrinkage or of controlledshrinkage at a temperature between 80 C. and 160 C., preferably between135-145 C., i.e., at a temperature which is the same as or only slightlythan the stretching temperature, for a time varying from a fraction of asecond to a few seconds, e.g., about 5 seconds.

The invention will be more readily understood by reference to theaccompanying drawing, in which FIGURE 1 is a diagrammatic showing ofapparatus suitable for use in stretching and annealing the yarns ofisotactic polypropylene.

FIGURE 2 is a fragmentary view of one element of the apparatus.

Referring to FIGURE 1, there is shown a roll 2, a heater 3, a secondroll 4, a second heater 5, a roll 6 and a winding system 7 of the ringtype.

In practice, the yarn (l in the drawing) passes over roll 2 into theheater 3 and thence over roll 4, being stretched between rolls 2 and 4which are rotated at different peripheral speeds to effect stretching ofthe yarn to the predetermined extent. For example, roll 2 may be rotatedat a peripheral speed of 415 m./minute, and roll 4 may be rotated at aperipheral speed of 20 to 100 m./minute, to impart the desired stretchto the yarn as it proceeds through heater 3. The stretched yarn thenpasses from roll 4 into the heater 5 and over roll 6 to the wind-up. Theperipheral speed of roll 6 may be lower (15%) than, the same as, orsomewhat higher than that of roll 4, so that the yarn passing throughheater is held against shrinkage or shrinks to a controlled extent.Rolls 2, and 6 may be driven by means of continuous speed-variators toadjust the stretching ratios. The rate of feed of the yarn to theheaters and the heating times are correlated so that at the selectedstretching and stabilizing temperatures, the desired objectives areaccomplished.

Heaters 3 and 5 may be heated in any suitable manner, for example by hotair, may have a length of, for instance 30 centimeters (for peripheralspeeds of the rolls within the ranges already stated), and are providedwith inlet and outlet openings as shown in FIGURE 2 for entry and exitof the yarn.

The heaters may be opened as shown at 8 in order to facilitate theintroduction of the yarn.

They can be obviously substituted by any equivalent heating medium asfor exampie a warm plate.

Alternatively, the stretched yarn may be stabilized against excessiveheat-shrinkage in two stages. Thus, the fibers or yarns may beheat-treated under conditions of controlled shrinkage between 0 andtwisted, wound on bobbins, and then given a further heat-treatment onthe bobbin, the second heat-treatment being preferably performed at atemperature somewhat higher than the first heat-treatment.

In practicing the latter embodiment, the heating time on the bobbin(second heat-stabilizing step) may be a few seconds or it may beincreased to about 60 minutes. The stabilized yarn obtained bycompleting the heattreatment on the bobbin has substantially the samecharacteristics as the yarn which is stretched and annealed continuouslyin what may be regarded as essentially a single-stage process.

The stretched and heat-stabilized yarn can be wound up withoutdiificulty, has satisfactory dimensional stability, and has improvedmechanical characteristics, as compared to the yarns which are notannealed under heating and conditions of controlled shrinking.

As mentioned above, and disclosed in the pending Natta et al.applications, 514,097, 514,098 and 514,099, filed June 8, 1955, theisotactic polypropylene produced by polymerizing propylene with the aidof the catalysts prepared from the transition metal compounds and themetal alkyls, may contain some atactic polypropylene. Such products maybe used in making fibers and yarns provided the content of atacticpolypropylene is not in excess of about 30%.

A close relationship exists between the residual shrinkage capacity ofthe stretched, stabilized yarns obtained by the present process and theamount of atactie polymer contained in the starting polypropylene fromwhich the fibers are formed. If the atactic polymer is 15% or less,stretched, annealed yarns which shrink only 01% in water at C. areusually obtained, whereas at higher atactic polymer contents, residualshrinkage of 34% may be regarded as a good result of the heattreatment.

The extent to which the yarn is allowed to shrink between the limits ofzero to 15 during the heat-stabilization is determined by the finalcharacteristics desired for the yarn. Thermal treatment of the yarnunder controlled shrinkage, which favors the return to a certaindisorder or irregularity of the molecular structure, results in a slightdecrease in the elastic characteristics of the yarn, a phenomenon whichis useful for certain applications of the yarn. On the other hand, whenthe thermal treatment of the stretched yarn is carried out underconditions such that the yarn is not free to shrink, or is even heldunder a slight tension, the heattreatment fixes the orientation of themolecules effected by the stretching and the elastic properties of theyarn are not substantially altered as a result of theheat-stabilization. This is generally advantageous for most purposes forwhich the yarn is to be used, but the yarn tends to shrink to a somewhathigher extent in water at 100 C. than when the yarn is allowed to shrinkto the limited controlled extent during the heat-treatment, otherconditions being equal.

In any event, the high elastic characteristics normally possessed by theisotactic polypropylene fibers and yarns are at most only slightlyreduced. The final yarn therefore is not only dimensionally stable, andeasy to wind, unwind, process and fabricate, but such stability isachieved without any substantial sacrifice of the desirable elasticproperties.

Whether the stretched yarn is free to shrink up to 15 during theheat-treatment, or is prevented from shrinking, the residual shrinkagecapacity is uniform along the length of the yarn and is not greater than34% as a maximum, which is acceptable and permits preparation of thecops and subsequent weaving operations to be carried out smoothly,without breaking of the yarn, and in the most satisfactory manner.

As noted, the extent to which the yarn shrinks during theheat-stabilization may be between zero and 15%. Increase in the percentshrinkage, within that range and up to the limit of 15 generally resultsin an increased elongation at break, the tenacity remaining almostconstant.

The following examples are given to illustrate the invention, it beingunderstood that these examples are not intended as limitative.

Example 1 Using the apparatus shown in FIGURE 1, yarn of polypropylenehaving an intrinsic viscosity of 0.9 and consisting of isotacticpolypropylene mixed with about 15% of atactic polypropylene, and havinga titer of 100 den. were processed in diiferent ways with the resultsshown in the table below, items 1-8. The yarns were- Stretched on a warmplate (yarns of items l3) After-stretched and stabilized undercontrolled shrinkage (yarns of items 4-6) Stretched and stabilized whileprevented from shrinking (yarn of item 7) and Stretched-and stabilizedunder'tension (yarn of item 8) Mechanical Character Alter Stretching andMechanical Oharac. after immersion in Setting boiling Water for 30 min.at free shrinking Rel. Tens. No V1 V2 V3 RS. Per- Per- T T Td cent centI II Shrin. Shrin.

R,g./ Elong. Percent R.E.I. R.E.R. M.E. R,g./ Elong. Percent R.E.I.R.E.R. den. Percent in H20 Percent Percent den. Percent in H2O PercentPercent M.E.

V =speed of roll 2 (m./min.).

Vi=speed of roll 4 (m./min.).

Va=speed of roll 6 (UL/111111.).

R.S. =stretcl1ing ratio. I

Rel. Percent=relaxation between rolls 4 and 6.

Tons. Percent=tension between rolls 4 and 6.

'1 I=temperature of the stretching medium.

'1 II=temperature oi the stretching medium between rolls 4 and 6. Td.=titer denier.

R=ultimete strength, gJden.

Elong. Percent=percent elongation at break.

Shrin. =shrinkage.

R.E.R. percent=perccnt recovery after a 10% strain of 5 minutes. R.E.I.percent=percent recovery after a 10% strain of 5 seconds. M.E.=elasticmodulus, gJden.

Example 2 The yarn processed had a tenacityof 0.7 g./den., an elongationof 580%, and a titer of 300 denier, and was obtained by melt-spinning anisotactic polypropylene having an intrinsic viscosity of 0.8 andcontaining about 12% of atactic polypropylene. Apparatus asshown in FIG-URE 1 was used.

The yarn was stretched between roll 2 (peripheral speed 4.5 m./min.) androll 4 (peripheral speed 27 m./min.) while passing through the warm airheater 8, having a length of 300 mm, and maintained at 130 C. Thestretched yarn was passed from roll 4 into warm air heater 5 (300 mm.long) maintained at 140 C., and thence to roll 6 rotating at aperipheral speed of 24.8 m./min. The yarn was thus allowed to shrink 8%during travel thereof between rolls 4 and 6. i

From roll 6 the shrunk, heat-stabilized yarn was passed to the twistingand winding device 7. The cop thus prepared was very regular and couldbe unwound without diflic-ulty. The final heat-stabilzed yarn had atenacity of 5.3 g./den., an elongation of 19%, and a titer of 30deniers. It shrank 3% when immersed in water at 100 C. for 30 minutes.

Example 3 The yarn processed had a tenacity of 0.8 g./den., anelongation of 610%, and a titer of 300 deniers. it was obtained bymelt-spinning a crystallizable polypropylene having an intrinsicviscosity of 0.95 and containing about 12% of atactic polypropylene.Using apparatus as shown in FIGURE 1, the yarn was stretched betweenroll 2 (peripheral speed 4 m;/min.) and roll 4 (peripheral speed 2 6m./min.) While passing through heater 3 having a length of 300 mm. andmaintained at 130 C. by hot air circulating therein.

From roll 4, the stretched yarn was passed to roll 6 (peripheral speed23.4 m./min.) thruogh the heater 5 maintained at 145 C. and 300 mm. inlength. The yarn was thus allowed to shrink 10% during the secondheattreatment.

The shrunk, heat-stabilized yarn was taken up on the dominant proportionof isotactic macromolecules and which is melt-spun to the fibers thatcan be processed by the present method may have, in general andpreferably, an intrinsic viscosity of 0.3 to 2.0. Such a polypropylenemay be obtained by separation from the polymerizate resulting frompolymerization of propylene with the catalysts aforesaid, by directpolymerization, or by heat-degradation of an isotactic polypropylenehaving a higher intrinsic viscosity.

Fibers formed by other methods, such as wetand dryspinning techniques,may also be stretched and heat-stabi lized against subsequent excessiveshrinkage by the present process, and either continuously or insuccessive stages.

Since some changes and variations may be made in the method asspecifically exemplified herein without departing from the spirit andscope of the invention it is to be understood that it is intended toinclude as part of this invention'such changes and variations as may beapparent to those skilled in the art.

What isv claimed is: In the manufacture of fibers of polypropylenecomprising crystal-lizable isotactic macromolecules and up to 15% ofamorphous, atactic, non-crystallizable macromolecules,

the method of orienting the fibers and then setting them in the orientedcondition while rendering them dimensionally stable without anysubstantial reduction in their elastic properties, which method consistsof the stepsof 1) passing the unor-iented fibers through a heating andstretching-for-orientation zone in which they are oriented by beingstretched 5 to 10 times their initial length while being heated, in theabsence of applied pressure, at a temperature of about C. withouteffecting any heatsetting of the fibers in said zone and (2.) thereafterintroducing the oriented fibers into an annealing zone in which, whilebeing maintained under a tension such that shrinkage thereof, if any, isheld to a maximum of 15%, the oriented fibers are heated at atemperature of from to C., and thereby set in the oriented condition,the annealing of the fibers being performed, at least in part, prior toany twisting or winding up of the fibers.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Ingersoll July 27, 1943 Stevenson Nov. 19,1946 Kline et a1. "May 27, 1947 Sisson Apr. 20, 1948 Hitt Nov. 30, 1948'Miles May 30, 1950 8 Merion et a1. Aug. 8, 1950 Averns et a1 Feb. 5,1952 Keen Feb. 16, 1954 Hasler Ian. 22, 1957 Natta et a1 Apr. 14, 1959Hunt et a1 Sept. 20, 1960 FOREIGN PATENTS Belgium Dec. 6, 1955

